1. Technical Field
The present invention relates to liquid crystal devices, driving methods for liquid crystal devices, and electronic apparatuses.
2. Related Art
Liquid crystal devices in which a liquid crystal layer is disposed between pixel electrodes and opposing electrodes have been known for some time. The pixel electrodes are electrically connected to switching elements such as thin-film transistors (referred to as “TFTs” hereinafter). The switching elements are controlled to turn on and off as the result of the input of scanning signals from scanning lines. When a switching element is on, a voltage from a data line is applied to the corresponding pixel electrode. As a result of this voltage, an electrical field is generated between the pixel electrode and the opposing electrode, and the liquid crystal layer is driven by these electrical fields.
A typical liquid crystal device employs, for example, inversion driving (AC driving), in which the polarity of the driving voltage applied to the pixel electrodes is inverted for each scanning line or data line, or is inverted for each frame in an image signal. In other words, the liquid crystal layer employs AC driving. In order to drive the liquid crystal layer using AC driving, for example, the opposing electrodes are held at a predetermined opposing electrode potential, and the potential of the pixel electrodes is switched between a high potential that is higher than the opposing electrode potential (positive polarity) and a low potential that is lower than the opposing electrode potential (negative polarity) over an interval of two consecutive frames. Doing so inverts the direction of the electrical field applied to the liquid crystal layer, which makes it possible to reduce electrical charge shift in the liquid crystal layer.
Reducing electrical charge shift makes it possible to reduce the DC voltage component applied to the liquid crystal layer due to the electrical charge shift, which in turn makes it possible to suppress the occurrence of display problems. In other words, a collapse in the balance between the positive and negative polarity electrical amounts caused by the DC voltage component is suppressed, which makes it difficult for flicker, caused by changes in the transmissivity of the liquid crystal device over a positive- and negative-polarity interval, to occur in the display image. Furthermore, it is difficult for the display to exhibit a constant display pattern (that is, burn-in) caused by the constant application of an electrical field to the liquid crystal layer resulting from the DC voltage component. However, the application of the DC voltage component has not been completely eliminated simply by carrying out inversion driving, and display problems have persisted.
Incidentally, it is known that driving a liquid crystal device with the difference between the opposing electrode potential and the high potential set to the same difference as the difference between the opposing electrode potential and the low potential will result in the occurrence of a DC voltage component. It is thought that this DC voltage component arises due to the following two phenomena.
The first phenomenon is a phenomenon in which when the switching element switches from on to off, the potential of the pixel electrode fluctuates due to the distribution of a charge in a channel region and the pixel electrode being charged (also called “field-through”, “push-down”, or “punch-through”). Specifically, the charge accumulated through parasitic capacitance and in a storage capacitor results in a phenomenon in which the pixel electrode voltage drops due to charge redistribution when the switching element is turned off.
The second phenomenon is a phenomenon in which electrical charge shift occurs when the electric properties on the pixel electrode side and the opposing electrode side of the liquid crystal layer are asymmetrical.
The generation of the DC voltage component due to the first phenomenon can be eliminated if the amount of fluctuation in the potential of the pixel electrode caused by the parasitic capacitance of the switching element is measured or estimated in advance and the opposing electrode potential is set so as to cancel out the fluctuation in the positive- and negative-polarity electrical amounts caused by this fluctuation amount.
The technique disclosed in JP-A-2007-219356 can be given as an example of a technique for eliminating the occurrence of the DC voltage component caused by the second phenomenon.
The liquid crystal device according to JP-A-2007-219356 includes liquid crystals held in a tilted vertical orientation mode between a first inorganic orientation film and a second inorganic orientation film, and a voltage application member. The thickness of the second inorganic orientation film is greater than the thickness of the first inorganic orientation film. The voltage application member applies a predetermined voltage so that the first inorganic orientation film is set to a first potential and the second inorganic orientation film is set to a second potential that is lower than the first potential.
According to the technique disclosed in JPA-2007-219356, different potentials are generated at the first inorganic orientation film and the second inorganic orientation film, and thus an effect in which electrical charge shift caused by the difference in the thicknesses of the first inorganic orientation film and the second inorganic orientation film are eliminated can be expected. However, electrical charge shift can be thought to occur due to other reasons aside from the difference in the thickness between the first inorganic orientation film and the second inorganic orientation film; therefore, from the standpoint of effectively reducing the DC voltage component through the configuration of the liquid crystal device, the technique disclosed in JP-A-2007-219356 has room for improvement.
Meanwhile, a driving method for a liquid crystal device that focuses on the aforementioned two phenomena has been proposed. For example, JP-A-2002-189460 discloses a technique that shifts the opposing electrode potential, which serves as the basis of the polarity inversion in inversion driving, in order to correct the influence of the first phenomenon (field-through) and the second phenomenon (voltage fluctuations caused by differences in the electric properties of the element substrate and the opposing substrate) in advance. Specifically, in JP-A-2002-189460, the amount of voltage fluctuation caused by the first phenomenon and the amount of voltage fluctuation caused by the second phenomenon are measured in an initial stage according to predetermined measurement conditions, and a value obtained by adding those amounts together is added, as a constant correction voltage, to a setting potential (Vcom) of the opposing electrodes.
According to the technique disclosed in JP-A-2002-189460, it is thought that adding the correction voltage obtained by adding the amounts of voltage fluctuation in the first phenomenon and the second phenomenon to the opposing electrode potential makes it possible to suppress a drop in the display quality caused by the occurrence of the DC voltage component.
However, in the case where the correction voltage for the second phenomenon is greater than the correction voltage for the first phenomenon to a certain degree, the opposing electrode potential will shift greatly in the positive or the negative direction. In other words, if the correction voltage for the second phenomenon is high, there will be a great amplitude change to the positive or the negative in the driving voltage. Accordingly, there are cases where display problems such as flicker or the like will arise.